Study On Electrochemical Preparation And Performance Of The Anode Catalysts For Alkaline Direct Methanol Fuel Cells

To achieve catalysts with high Pt utilization, high activity and stability for methanol oxidation reaction(MOR) in alkaline media, Pt-on-Au/CNTs catalysts are synthesized through site-selective electrodeposition and analyze activity and catalytic mechanism. To investigate the possibility of replacing Pt with Pd, Pd-on-Au/CNTs are synthesized through site-selective electrodeposition and compare activity and stability with Pt-on-Au/CNTs.Then design Pt-on-Pd catalysts which exhibit better activity and stability than Pt/CNTs, Pd/CNTs towards oxidation of methanol and ethanol in alkaline media.Several Pt-on-Au/Sn O2-CNTs catalysts with different Pt loadings are synthesized through site-selective electrodeposition for catalytic methanol oxidation reaction(MOR) in alkaline media. The catalysts are tested to exhibit extremely high Pt mass activity towards MOR, and the catalytic mechanism is proposed based on the synergetic effect between Pt and Au, in which the Pt entities provide Pt-OH for oxidation of alkoxide(CH3O-) while the Au surfaces provide adsorption sites for alkoxide.To further improve activity and stability of the catalysts and understand catalytic mechanism,several catalysts such as Pt-on-Au/CNTs, Pd-on-Au/CNTs, Pt-on-Pd-on-Au/CNTs, Pt-on-Pd/CNTs, and Pd-on-Pt/CNTs are synthesized mainly through electrodeposition method.The activity and stability comparisons show that Pt-on-Au/CNTs has a higher MOR activity but a lower stability than Pd-on-Au/CNTs.To utilize the merits of the Pt and Pd components, Pt-on-Pd-on-Au/CNTs and Pt-on-Pd/CNTs catalysts are synthesized.The Pt-on-Pd-on-Au/CNTs and Pt-on-Pd/CNTs catalysts shows higher MOR activity than Pd-on-Au/CNTs and Pd/CNTs catalysts and higher stability than Pt-on-Au/CNTs, suggesting a synergistic interaction between Pt and Pd in catalyzing methanol oxidation reaction. Calculation shows that the total mass activity of Pt-on-Pd/CNTs with quite low Pt amount is on a similar level as that of Pt/CNTs for MOR oxidation.To develop applications of catalysts for other fuels in alkaline media,Pt/CNTs and Pd/CNTs catalysts are tested towards methanol,ethanol and potassium formate varing with temperature,and the result indicates that the activity toward methanol growed fastest no matter on Pt/CNTs or Pd/CNTs with temperature. Pt is more active than Pd for methanol or ethanol oxidation but Pt deactivation is more severe during ethanol oxidation compared with Pd deactivation. The oxidation peak current and chronoamperometry of Pt-on-Pd catalyst in methanol or ethanol are higher than Pt or Pd, which implys that Pt-on-Pd catalyst has a higher activity than Pd and a better stability than Pt.